How to remove some columns from an existing table?

Question

Let's say my table's structure is as follows:
Table name: EMPLOYEE
Columns: Name, Birthdate, Gender, Salary, Hometown, Language and so on.
There are data in the table. Now I want to remove columns Hometown and Language, and I don't care the data loss. Also, there is no constraint.
What's the sql command to do this? Thanks!

Answer 1

I think you need to be a bit more specific than stating that something is not correct.
It is perfectly correct and proper to drop a column from a table even when there is data. The problem comes when you need to drop a column and the window you have to perform the expensive operation of actually reclaiming the disk space is insufficient. If that is the case (and there is no indication from the original poster that is the case, but it's certainly conceivable), it may make sense to mark the column as unused, which is a quick update to the data dictionary and then drop the unused columns at a later date when you have a larger window. This is incredibly useful in a handful of larger systems, but not particularly necessary in most systems most of the time. It wouldn't make sense to mark a column unused and then immediately drop the column.
If you are going to go the SET UNUSED route, your syntax is incorrect. Once you mark the column unused, you can't drop the column by name any longer (since you can add a column with the unused column's old name, it's also potentially rather dangerous). You have to use the DROP UNUSED COLUMNS clause
SQL> desc x;
Name                                      Null?    Type
COL1                                      NOT NULL NUMBER
COL2                                               NUMBER
SQL> alter table x set unused column col2;
Table altered.
SQL> alter table x drop column col2;
alter table x drop column col2
ERROR at line 1:
ORA-00904: "COL2": invalid identifier
SQL> alter table x drop unused columns;
Table altered.Justin